During cruising conditions in cold weather, ice may form in the engine throttle body, intake manifold, and positive crankcase ventilation (PCV) valve. Engine exhaust gases may blow by the pistons into the crankcase and are then vented into the throttle body or intake manifold through the PCV valve. The exhaust gases may contain water vapor which may freeze, especially in trucks during cold weather cruising conditions where cold air sweeping across the engine compartment may keep the throttle body and intake manifold below freezing temperatures.
Ice may remain in the throttle body and intake manifold after engine shutoff. If ice remains during a subsequent engine start, it may melt and the resulting water may cause engine misfires until the water is cleared out. An onboard engine misfire diagnostic routine operated by the engine controller may then indicate a misfire fault requiring maintenance even though the engine was operating properly.
U.S. Pat. No. 8,170,772 and U.S. published patent application 2012/0244994 disclose inferring ice buildup based on temperature. In response to ice detection engine speed is increased to reduce engine sensitivity to poor air/fuel mixtures caused by melted ice and resulting misfire. The inventors herein have recognized, however, that these references do not address onboard engine misfire diagnosis and false misfire indications.
Another approach has been to infer ice buildup and then delay misfire diagnosis after engine start for a predetermined time to allow the ice to melt. The inventors herein have recognized that this approach may result in delaying misfire diagnosis unnecessarily after ice has melted and dissipated. In one aspect of the invention disclosed herein, the inventors have solved these problems by inferring whether ice has formed in the engine intake manifold or throttle body in response to engine operating parameters, inferring whether the ice has melted after an engine shutoff, then inferring whether the melted ice has dissipated, and enabling engine misfire diagnostics after engine start in response to the inference of dissipated melted ice. In this manner misfire diagnosis may not be delayed unnecessarily. Instead misfire detection will be delayed only after there is an actual indication or inference that there was ice which has melted, but not dissipated through evaporation and/or leakage through the manifold. Any delay in misfire diagnosis therefore only occurs when actually necessary and only for a minimal time.
In another aspect of the invention, the inventors estimate the amount of ice formed to further reduce the average delay of misfire diagnosis. In still another aspect of the invention, the inventors have facilitated ice melting and dissipation by coupling engine heat to the intake manifold or throttle body.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.